What does this MR do and why?

Creates Ai::DailyFlowOnPushWorker and extends Git::BranchHooksService via EE prepend to trigger the SDLC Context Agent on default-branch pushes with a 24-hour ExclusiveLease debounce, so the agent can run automatically in production instead of being dead code.

References

• Project epic: https://gitlab.com/groups/gitlab-org/-/work_items/21005+s
  • Phase epic: https://gitlab.com/groups/gitlab-org/-/work_items/22715+s
  • Closes https://gitlab.com/gitlab-org/gitlab/-/work_items/605272+s
• Design issue: https://gitlab.com/gitlab-org/gitlab/-/work_items/600861+s
• Next issue (composite identity): https://gitlab.com/gitlab-org/gitlab/-/work_items/605273+s
• Feature flag rollout: https://gitlab.com/gitlab-org/gitlab/-/work_items/605274+s

MR acceptance checklist

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